twofish.cpp

// twofish.cpp - modified by Wei Dai from Matthew Skala's twofish.c
// The original code and all modifications are in the public domain.
 
#include "pch.h"
#include "twofish.h"
#include "secblock.h"
#include "misc.h"
 
NAMESPACE_BEGIN(CryptoPP)
 
// compute (c * x^4) mod (x^4 + (a + 1/a) * x^3 + a * x^2 + (a + 1/a) * x + 1)
// over GF(256)
static inline unsigned int Mod(unsigned int c)
{
    static const unsigned int modulus = 0x14d;
    unsigned int c2 = (c<<1) ^ ((c & 0x80) ? modulus : 0);
    unsigned int c1 = c2 ^ (c>>1) ^ ((c & 1) ? (modulus>>1) : 0);
    return c | (c1 << 8) | (c2 << 16) | (c1 << 24);
}
 
// compute RS(12,8) code with the above polynomial as generator
// this is equivalent to multiplying by the RS matrix
static word32 ReedSolomon(word32 high, word32 low)
{
    for (unsigned int i=0; i<8; i++)
    {
        high = Mod(high>>24) ^ (high<<8) ^ (low>>24);
        low <<= 8;
    }
    return high;
}
 
inline word32 Twofish::Base::h0(word32 x, const word32 *key, unsigned int kLen)
{
    x = x | (x<<8) | (x<<16) | (x<<24);
    switch(kLen)
    {
#define Q(a, b, c, d, t) q[a][GETBYTE(t,0)] ^ (q[b][GETBYTE(t,1)] << 8) ^ (q[c][GETBYTE(t,2)] << 16) ^ (q[d][GETBYTE(t,3)] << 24)
    case 4: x = Q(1, 0, 0, 1, x) ^ key[6];
    // fall through
    case 3: x = Q(1, 1, 0, 0, x) ^ key[4];
    // fall through
    case 2: x = Q(0, 1, 0, 1, x) ^ key[2];
            x = Q(0, 0, 1, 1, x) ^ key[0];
    }
    return x;
}
 
inline word32 Twofish::Base::h(word32 x, const word32 *key, unsigned int kLen)
{
    x = h0(x, key, kLen);
    return mds[0][GETBYTE(x,0)] ^ mds[1][GETBYTE(x,1)] ^ mds[2][GETBYTE(x,2)] ^ mds[3][GETBYTE(x,3)];
}
 
void Twofish::Base::UncheckedSetKey(const byte *userKey, unsigned int keylength, const NameValuePairs &)
{
    AssertValidKeyLength(keylength);
 
    unsigned int len = (keylength <= 16 ? 2 : (keylength <= 24 ? 3 : 4));
    SecBlock<word32> key(len*2);
    GetUserKey(LITTLE_ENDIAN_ORDER, key.begin(), len*2, userKey, keylength);
 
    unsigned int i;
    for (i=0; i<40; i+=2)
    {
        word32 a = h(i, key, len);
        word32 b = rotlConstant<8>(h(i + 1, key + 1, len));
        m_k[i] = a+b;
        m_k[i + 1] = rotlConstant<9>(a + 2 * b);
    }
 
    SecBlock<word32> svec(2*len);
    for (i=0; i<len; i++)
        svec[2*(len-i-1)] = ReedSolomon(key[2*i+1], key[2*i]);
    for (i=0; i<256; i++)
    {
        word32 t = h0(i, svec, len);
        m_s[0*256+i] = mds[0][GETBYTE(t, 0)];
        m_s[1*256+i] = mds[1][GETBYTE(t, 1)];
        m_s[2*256+i] = mds[2][GETBYTE(t, 2)];
        m_s[3*256+i] = mds[3][GETBYTE(t, 3)];
    }
}
 
#define G1(x) (m_s[0*256+GETBYTE(x,0)] ^ m_s[1*256+GETBYTE(x,1)] ^ m_s[2*256+GETBYTE(x,2)] ^ m_s[3*256+GETBYTE(x,3)])
#define G2(x) (m_s[0*256+GETBYTE(x,3)] ^ m_s[1*256+GETBYTE(x,0)] ^ m_s[2*256+GETBYTE(x,1)] ^ m_s[3*256+GETBYTE(x,2)])
 
#define ENCROUND(n, a, b, c, d) \
    x = G1 (a); y = G2 (b); \
    x += y; y += x + k[2 * (n) + 1]; \
    (c) ^= x + k[2 * (n)]; \
    (c) = rotrConstant<1>(c); \
    (d) = rotlConstant<1>(d) ^ y
 
#define ENCCYCLE(n) \
    ENCROUND (2 * (n), a, b, c, d); \
    ENCROUND (2 * (n) + 1, c, d, a, b)
 
#define DECROUND(n, a, b, c, d) \
    x = G1 (a); y = G2 (b); \
    x += y; y += x; \
    (d) ^= y + k[2 * (n) + 1]; \
    (d) = rotrConstant<1>(d); \
    (c) = rotlConstant<1>(c); \
    (c) ^= (x + k[2 * (n)])
 
#define DECCYCLE(n) \
    DECROUND (2 * (n) + 1, c, d, a, b); \
    DECROUND (2 * (n), a, b, c, d)
 
typedef BlockGetAndPut<word32, LittleEndian> Block;
 
void Twofish::Enc::ProcessAndXorBlock(const byte *inBlock, const byte *xorBlock, byte *outBlock) const
{
    word32 x, y, a, b, c, d;
 
    Block::Get(inBlock)(a)(b)(c)(d);
 
    a ^= m_k[0];
    b ^= m_k[1];
    c ^= m_k[2];
    d ^= m_k[3];
 
    const word32 *k = m_k+8;
    ENCCYCLE (0);
    ENCCYCLE (1);
    ENCCYCLE (2);
    ENCCYCLE (3);
    ENCCYCLE (4);
    ENCCYCLE (5);
    ENCCYCLE (6);
    ENCCYCLE (7);
 
    c ^= m_k[4];
    d ^= m_k[5];
    a ^= m_k[6];
    b ^= m_k[7];
 
    Block::Put(xorBlock, outBlock)(c)(d)(a)(b);
}
 
void Twofish::Dec::ProcessAndXorBlock(const byte *inBlock, const byte *xorBlock, byte *outBlock) const
{
    word32 x, y, a, b, c, d;
 
    Block::Get(inBlock)(c)(d)(a)(b);
 
    c ^= m_k[4];
    d ^= m_k[5];
    a ^= m_k[6];
    b ^= m_k[7];
 
    const word32 *k = m_k+8;
    DECCYCLE (7);
    DECCYCLE (6);
    DECCYCLE (5);
    DECCYCLE (4);
    DECCYCLE (3);
    DECCYCLE (2);
    DECCYCLE (1);
    DECCYCLE (0);
 
    a ^= m_k[0];
    b ^= m_k[1];
    c ^= m_k[2];
    d ^= m_k[3];
 
    Block::Put(xorBlock, outBlock)(a)(b)(c)(d);
}
 
NAMESPACE_END